The invention relates to integrated circuits, and more particularly, to electrostatic discharge protection circuits.
Electrostatic discharge (ESD) voltage and current can be a major source of damage for integrated circuits. ESD can be a problem with an integrated circuit that is not in operation or coupled to a circuit. At these times, many of the integrated circuit""s external connections are floating and exposed to damage. The potential for ESD damage has become even more of a predominant issue with the decreasing device sizes, spacing, and operating voltages of modem components, all of which has the effect of increasing the likelihood of an ESD event causing damage.
The primary object of most common types of ESD protection is to isolate vulnerable internal circuitry from an ESD event. An integrated circuit connects to its external environment through interconnect pads (also referred to as die terminals, bond pads, die pads, or contact pads). Typically an ESD protection circuit is incorporated at, or shortly after, the interconnect pad in an integrated circuit and contains breakdown devices and current limiting devices that provide an alternative and more durable path for the damaging ESD voltage and current to flow through. ESD protection circuitry, however, while necessary for ESD event survival, can interfere with signal transmission speed and increase capacitive loading when the integrated circuit is operation. Therefore in ESD protection circuitry a balance is sought which preserves signal speed while not over exposing the integrated circuit to damage from ESD.
Various techniques have been utilized in constructing ESD protection circuits for integrated circuits and are well know to those skilled in the art. One such common ESD technique is to incorporate an input buffer of more durable circuit components between the interconnect pad and the internal active circuitry that is capable of better absorbing the elevated potentials of a given ESD event. However, these heavier duty components typically also have a higher input drive requirements and corresponding signal propagation delays that can become unacceptable to the design specifications of the integrated circuit. Another technique is to incorporate one or more clamping diodes or other such breakdown circuits that couple an ESD event to a discharge path away from the more damage susceptible input components. A further technique is to incorporate xe2x80x9cguard ringsxe2x80x9d of opposite carrier, or over doped similar carrier, semiconductor that form a protecting diode or conduction path system around the input circuitry and interconnect pads.
A common ESD protection technique is to incorporate a resistance into the integrated circuit input just after the interconnect pad. One of the effects of this input resistance has is to current limit the ESD event. An ESD damping input resistance incorporated at the interconnect pad helps dissipate an ESD event quickly and contain it near the interconnect pad. Unfortunately, this technique can cause a significant signal propagation delay issue by adding a higher RC time constant when the ESD input resistance is combined with the capacitive load of the input circuit and interconnect line. Unless the external drive of the integrated circuit input is made larger, it now will take longer to charge the input interconnect""s capacitive load through the ESD protection resistance. The reduction in device and feature size in modern integrated circuits has increased resistance of the interconnect lines themselves to become a significant factor in the total input resistance. These interconnect line resistances add to the ESD resistance giving a larger effective input resistance than intended. Furthermore, the interconnect resistances tend to be of variable size, as the input interconnect lines are of differing lengths and cross section. This leads to issues of varying RC time delay on different input lines, a significant issue in high speed and synchronous design.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a system to reduce signal delay from ESD. Additionally there is a need for the ability to have matched delays or resistances across inputs.
The above-mentioned problems with ESD input resistance and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
In one embodiment, an integrated circuit comprises an interconnect pad, an interconnect line having a first end coupled to the interconnect pad, a resistor coupled to an opposite second end of the interconnect line, wherein the resistor is adjusted to compensate for an inherent resistance of the interconnect line, and an electrostatic protection circuit coupled to the resistor.
A method for coupling an external signal to the input of an integrated circuit comprises receiving an external signal at an interconnect pad, coupling the signal to a conductor line, coupling the signal from the conductor line to a resistor, wherein the resistor has been selectively adjusted to compensate for an internal resistance of the conductor line, coupling the resistor to an electrostatic protection circuit, and coupling the signal from the resistor to an internal circuit.
Another method of adjusting an integrated circuit for a specific input resistance comprises coupling an interconnect pad to an interconnect line, coupling the interconnect line to a resistor, coupling the resistor to an internal circuit of the integrated circuit, coupling the resistor to an electrostatic protection circuit, and adjusting the resistor to achieve a specific input resistance for the integrated circuit and compensate for a resistance of the interconnect line.
In a further method of adjusting an integrated circuit for a specific input RC time constant comprises coupling an interconnect pad to an interconnect line, coupling the interconnect line to a resistor, coupling the resistor to an internal circuit of the integrated circuit, adjusting the resistor to achieve the specific input RC time constant for the integrated circuit, compensating for a resistance and capacitance of the interconnect line, and coupling the resistor to an electrostatic protection circuit.
In another embodiment a memory device comprises an address interface coupled to a first interconnect pad circuit, a first interconnect circuit coupled to the first interconnect pad circuit, a first resistor circuit coupled to the first interconnect circuit, wherein the first resistor circuit is adjusted to compensate for a resistance of the first interconnect circuit, a data interface coupled to a second interconnect pad circuit, a second interconnect circuit coupled to the second interconnect pad circuit, a second resistor circuit coupled to the second interconnect circuit, wherein the second resistor circuit is adjusted to compensate for a resistance of the second interconnect circuit, a control interface coupled to a third interconnect pad circuit, a third interconnect circuit coupled to the third interconnect pad circuit, and a third resistor circuit coupled to the third interconnect circuit, wherein the third resistor circuit is adjusted to compensate for a resistance of the third interconnect circuit.
In a further embodiment, an electrostatic discharge protection circuit comprises an interconnect pad coupled to a conductor, a resistor coupled to the conductor, wherein the resistor is adjusted to compensate for a resistance of the conductor such that the combined resistance of the resistor and the resistance of the conductor are substantially equal to a predefined value, and an electrostatic discharge circuit coupled to the resistor.
In yet another embodiment an integrated circuit comprises a first interconnect pad, a second interconnect pad, a first interconnect line having a first end coupled to the first interconnect pad, a second interconnect line having a first end coupled to the second interconnect pad, a first resistor, R1, coupled to an opposite second end of the first interconnect line, where the first resistor is adjusted to compensate for an inherent resistance of the first interconnect line, RL1, a second resistor, R2, coupled to an opposite second end of the second interconnect line, where the second resistor is adjusted to compensate for an inherent resistance of the second interconnect line, RL2, and such that R1+RL1=R2+RL2, a first electrostatic protection circuit coupled to the first resistor, and a second electrostatic protection circuit coupled to the second resistor.
In another embodiment an integrated circuit comprises first and second interconnect pads, a first interconnect line having a line resistance of RL1, a line capacitance of CL1, and a first end coupled to the first interconnect pad, a second interconnect line having a line resistance of RL2, a line capacitance of CL2, and a first end coupled to the second interconnect pad, a first resistor, R1, coupled to an opposite second end of the first interconnect line, where a value of the first resistor is selected to set a first input RC time constant in combination with the first interconnect line, where the first input RC time constant is (R1+RL1)CL1, a second resistor, R2, coupled to an opposite second end of the second interconnect line, where the second resistor is selected to set a second input RC time constant in combination with the second interconnect line, where the second input RC time constant is (R2+RL2)CL2, and such that (R1+RL1)CL2=(R2+RL2)CL2, a first selectable electrostatic discharge path coupled to the first resistor, and a second selectable electrostatic discharge path coupled to the second resistor.